The duo will be expected to challenge Ainsley Maitland-Niles and Sead Kolasinac for starting berths as they make their way into the first team squad.

Tierney was signed from Celtic in the summer after a protracted transfer saga. The Gunners saw two bids rejected by the Scottish champions before getting the deal over the line for £25 million ($30m).

The 22-year-old left back arrived in London with a niggling knee injury and is also recovering from double hernia surgery he underwent over the summer. The Scotland international has not played since May.

Bellerin is an even longer-term absentee. The Spain international speedster has been out since January with a cruciate ligament injury suffered in a Premier League clash with Chelsea.

The 24-year-old Barcelona youth product has made 146 appearances for Arsenal and had been hugely impressive before his injury setback last season.

Neither man will be in contention to face Watford on Sunday but their return to training will buoy the Arsenal faithful.

One man who could be in line for a return to the line-up for the clash with the Hornets is Rob Holding.

The central defender had been looking like cementing a place in Emery’s starting line up in the early stages of the 2018-19 season.

He made 15 starts before he too suffered a cruciate ligament injury, just a few weeks before Bellerin.

Holding was ruled out for the season after a clash with Manchester United’s Marcus Rashford.

The return of the trio will offset the loss of two defensive stalwarts at the Emirates. Former club captain Laurent Koscielny has left the club for Bordeaux, while veteran Nacho Monreal has moved to Real Sociedad in his native Spain.